The secrets of Harley-Davidson's new engine: the Milwaukee Eight M8

As every year, the time is approaching (late August) when Harley-Davidson unveils next year's new models. Although so far, it's all rumors, it appears that the new Milwaukee Eight engine, currently installed in the Touring models, will power the entire 2018 Big Twin lineup.

Let's review the technical details and features of this new M8 engine, which the Motor Company launched a year ago and powers the 2017 Touring model range and likely the rest of the brand's Big Twin models in the coming years.
Named the Milwaukee-Eight in honor of one of its main innovations, the use of 8 valves in the cylinder heads, it offers more torque and power than its predecessors without losing the "heritage" of its iconic image, maintaining the 45º angle between the cylinders.

The new M8 is the ninth engine in the Big Twin series:
Atmospheric-Twin (1909)
F-Head (1911)
Flathead (1929)
Knucklehead (1936)
Panhead (1948)
Shovelhead (1966)
Evolution (1984)
Twin-Cam (1999)
Milwaukee-Eight (2017)

Engine capacities and models
The Milwaukee-Eight is introduced in 2017 in three versions:
107ci (1745cc) with oil-cooled cylinder heads (Precision Cooling) for Street Glide Special, Road Glide Special, Road King/Road King Classic and Freewheeler models.
107ci (1745cc) with water-cooled (Twin-Cooled) cylinder heads for Ultra Limited/Ultra Limited Low, Road Glide Ultra and Tri Glide Ultra models.
114ci (1870cc) with water-cooled (Twin-Cooled) cylinder heads for the exclusive Custom Vehicle Operations CVO Limited and CVO Street Glide models.

Twin-Cam on steroids?
Although at first glance the exterior looks quite similar to its Twin-Cam predecessor, the truth is that this new engine has been completely redesigned from the ground up, improving the strengths of previous models and correcting the shortcomings caused by the constant increases in displacement and power of recent years. Let's review the main changes:

• More power: The M8 has 11% more torque, which, together with the larger displacement, provides significantly higher power and performance.
• More acceleration: The M8 weighs the same as its predecessor and when this is added to its power increase, the result is 11% faster acceleration than the 103ci Twin-Cam.
• Reduced consumption: Thanks to the use of two spark plugs per cylinder, optimized ignition, and high-flow cylinder heads with four valves per cylinder, engine efficiency is improved, reducing fuel consumption.
• Improved temperature management: The new design has managed to keep the heat inside the engine (where it should be) by reducing the temperature absorption of the cylinders and cylinder heads, aided by cooling (with oil or water) at the hottest points of the cylinders.
• Greater Rider Comfort: A new, slimmer primary transmission cover and a lowered air cleaner cover improve rider legroom around the engine, making ground access easier for many riders. All Milwaukee-Eight models feature improved hydraulic "Assist and Slip" clutch actuation, which reduces lever effort by 7%.
• Pleasant vibrations: For the first time, a balance shaft has been mounted inside the engine, connected to the chassis by silent blocks, providing unprecedented smoothness without losing "character."
• Enhanced exhaust note: Many of the engine changes have been aimed at minimizing engine interior noise in order to enhance the exhaust note while meeting noise emission regulations. As was said when the Evolution engine was introduced, "We're reducing the noise so we can increase the music."
• Improved electrical charging: Modern motorcycles are increasingly equipped with more electrical and electronic devices (engine management, audio and multimedia, heating, lights, etc.), so a new alternator has been installed that provides 50% more power at idle to meet these and future electrical demands.
• Refreshed exterior design: Engineers have sought to respond to the aesthetic demands of loyal customers by giving the M8 a "muscular" look, wrapping the mechanical parts more directly, like mechanical skin, allowing us to glimpse the components hidden beneath the covers. The surface area of the cooling fins has also been increased, providing greater functionality and creating a more massive look.

Technology and tradition
The goal wasn't simple: replace a well-functioning engine and meet the demands of modern customers in a globalized market, creating a refined product that meets expectations in terms of quality and brand heritage, all at a price competitive among premium products. To achieve this and all the aforementioned points while increasing reliability and meeting the strictest regulations for different markets, Harley-Davidson engineers faced numerous mechanical design challenges that were solved in a variety of ways, leveraging the experience of a brand with more than 100 years of history and applying the latest manufacturing technologies.

Eight valves, four spark plugs... and one camshaft
The addition of four valves per cylinder achieves several objectives simultaneously. This system creates a flatter combustion chamber (with a smaller surface area and therefore less heat absorption), increases compression ratio to 10.5:1, and increases air intake and exhaust flow by 50%. The valves are hydraulically actuated, as in previous models, requiring no adjustment and allowing the use of lighter springs than those of previous models.
The hydraulic lifters are moved by a single camshaft (as in the Evolution and earlier models) driven by a chain from the crankshaft and adjusted by a hydraulic tensioner. The choice of a single camshaft simplifies the mechanics and reduces friction and unwanted noise.
With two spark plugs per cylinder head, we achieve improved and faster combustion, while simultaneously increasing efficiency and fuel consumption. Two sensors (one in each cylinder head) have also been installed to capture engine vibrations for better ignition timing, advancing ignition timing as far as possible without knocking or detonation. This system replaces the previous "Ion Sense" and has higher resolution, working in conjunction with the ECU programming to ensure the most complete combustion possible.
The cylinder head cooling systems inherited from Project Rushmore have been reused, providing internal passages to the points where the most heat builds up, and passing oil or water through them, depending on the model. Both the oil and water pumps have been redesigned to move a higher volume per minute, and idle speeds have now been lowered from 1,000 rpm to 850 rpm.
As we mentioned earlier, one way to prevent the engine from accumulating excessive heat is to expel combustion gases as quickly as possible. Along with the larger valve surface area and optimized ignition timing, the new exhaust design with the relocated catalytic converter facilitates this task more effectively, directing radiated heat away from the driver and passenger.

Reinforcing the foundations
Obviously, the increases in displacement and torque must be accompanied by a reinforced engine underbody. The crankshaft has been oversized, and the bearings are able to withstand greater loads. The new crankcase is 23% stronger than the previous one, yet weighs the same. This has been made possible by removing unnecessary material, giving the appearance that the covers now "hug" the internal parts, following their shape.
The new counterbalance shaft consists of a mass that rotates in the opposite direction to the crankshaft, absorbing a large part of the vibrations emitted by it.
Another challenge in a large-displacement, dry-sump engine is the evacuation of pressure when the pistons move down. To this end, new engine breathers have been created that more efficiently separate air from the suspended oil and connect to the transmission sump, preventing condensation from forming in the air filter, as was often the case in previous engines.

Primary and transmission at engine level
With the increase in displacement, improvements to the primary transmission are required. Converting the brutal torque generated by the pulses of two enormous pistons moving up and down into a smooth, controlled rotary motion is no easy task, unless a massive crankshaft is used, which reduces efficiency. In this case, the primary transmission has been redesigned, improving the ramps and mounting of the balancer and adopting a centrifugal force-assisted clutch, which is smooth at idle and progressively strengthens as acceleration is achieved, reducing clutch lever effort (with a Brembo hydraulic pump) by 7% without losing power. At the same time, this device will prevent the rear wheel from locking up during sudden deceleration (anti-lock clutch).
The starter motor is now more powerful, increasing from 1.2 kW to 1.6 kW, and the solenoid has been modernized. The ECM assists during starting by activating decompressors located in the cylinder heads and adjusting the ignition timing accordingly.
As for the transmission, one of the main new features also relates to the elimination of internal noise, for which a "constant contact" system has been used in some of the gears to eliminate backlash between them and improve synchronization.

SDBV Suspensions
One of the most requested features by potential Harley-Davidson touring model owners in markets outside the United States is improved suspension, both in terms of vehicle handling and ride comfort. The design team has introduced a completely new system that allows for quick and easy preload adjustments up to 30% greater than previous models.
The front suspension has a new "Showa dual bending valve" suspension technology with the damping performance of a competition cartridge fork, with a
More linear behavior and less weight. This basically means that the fork adapts its stiffness and performance in real time, "detecting" changes in the ground surface or driving speed.

Screamin' Eagle
As expected, HD's (Screamin' Eagle) high-performance boost and accessories catalog now includes a multitude of components and kits to turn the M8 into an adrenaline-pumping powerhouse. We can find everything from approved, higher-performance exhausts and air filters to boost "Stages" that will transform the Milwaukee Eight, up to 117ci (1917cc).

Conclusions
When judging a new product of this type, we must do so based on current circumstances and evolving global market needs. Harley-Davidson needed to update its product after 17 years under very restrictive regulations that make it very difficult to homologate a large-displacement, dry-sump, air-cooled engine while maintaining the brand's traditional aesthetic. New customers demand modernity, power, smoothness, and reliability, but with minimalism and a retro tradition.
It seems Harley-Davidson has risen to the occasion once again, surprising with a powerful engine that meets a wide variety of requirements with devastating balance. Here's to many more years to come.

Frank Burguera

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